Concerning the relationship between benefit and radiation risk, and cancers detected and induced, in a breast screening programme.

In a breast screening programme based upon X-ray mammography it is necessary to demonstrate that benefit, from reduced mortality arising from earlier diagnosis, exceeds any potential risk from future induction of breast cancers by ionizing radiation. A rigorous treatment of this problem would be both complex and subject to large statistical uncertainty, even if all necessary data were available. A more simplified approach is to show that the number of cancers detected exceeds the number potentially induced by a sufficient margin. These numbers are relatively well established, but this approach is less satisfactory owing to the question of what would constitute a sufficient margin. This paper attempts to explore a possible relationship between the detection/induction ratio and the benefit/risk ratio, using treatment outcome data from three independent sources and mortality reduction data. Agreement between these four sources is considered to be fair, given the nature of the data. The future screening of older women (over 65 years) is also found to have a significant effect on the final outcome. When current trends in such screening are allowed for, the benefit/risk ratio is found to be only marginally less than the detection/induction ratio.